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Re: [Help-glpk] Assertion failed
From: |
Andrew Makhorin |
Subject: |
Re: [Help-glpk] Assertion failed |
Date: |
Fri, 14 Jul 2006 04:45:30 +0400 |
> I have a problem with running glpk-4.10:
>
> I run the following MIP instance using command (glpsol --cpxlp
> ~/tmp_prob.lp):
>
> Minimize
> obj: x_1
>
> Subject To
> r_1: - 1003 x_1 + x_2 >= 0
> r_2: - 1999 x_2 + x_3 >= 0
> r_3: - 4000 x_3 + x_4 >= 0
> r_4: + 8000 x_4 + x_5 <= 0
> r_5: + 2 x_5 + x_6 >= 0
> r_6: - x_1 <= -1002
> r_7: - x_2 <= -1005006
> r_8: - x_3 <= 138476654
> r_9: - x_4 <= -144165184
> r_10: - x_6 <= -1
>
> Bounds
> x_1 free
> x_2 free
> x_3 free
> x_4 free
> x_5 free
> x_6 free
>
> Generals
> x_1
> x_2
> x_3
> x_4
> x_5
> x_6
>
> End
>
> and I get the following output (error):
>
> lpx_read_cpxlp: 10 rows, 6 columns, 15 non-zeros
> lpx_read_cpxlp: 6 integer columns, none of which are binary
> lpx_read_cpxlp: 32 lines were read
> lpx_simplex: original LP has 10 rows, 6 columns, 15 non-zeros
> lpx_simplex: presolved LP has 5 rows, 6 columns, 10 non-zeros
> lpx_adv_basis: size of triangular part = 5
> 0: objval = 1.002000000e+03 infeas = 1.000000000e-00 (0)
> Assertion failed: spx->p != 0; file glpspx2.c; line 668
>
> It seems like an error in glpk or is there anything I should do to be able
> to
> solve this problem?
The error is caused by extremely bad properties of your problem.
Using free integral variables is a not good idea. Besides, as it
follows, for example, from constraint r_9, x4 being declared as
integral variable must be greater than 144165184; it is very
problematic for any solver based on finite precision arithmetic
to satisfy such condition.
Try to reformulate your problem. In particular, if a value of some
variable is expected to be greater than 100 in optimal solution,
there is no reason in most cases to consider it as integral.
Andrew Makhorin